Glass composition for protecting semiconductor junction, method of manufacturing semiconductor device and semiconductor device

ABSTRACT

A glass composition for protecting a semiconductor junction is made of fine glass particles prepared from a material in a molten state obtained by melting a glass raw material which contains at least ZnO, SiO 2 , B 2 O 3 , Al 2 O 3  and at least two oxides of alkaline earth metals selected from a group consisting of BaO, CaO and MgO and substantially contains none of Pb, As, Sb, Li, Na and K, the glass composition for protecting a semiconductor junction containing no filler.

RELATED APPLICATIONS

The present application is a National Phase of International ApplicationNumber PCT/JP2013/059761, filed Mar. 29, 2013.

TECHNICAL FIELD

The present invention relates to a glass composition for protecting asemiconductor junction, a method of manufacturing a semiconductor deviceand such a semiconductor device.

BACKGROUND ART

There has been known a method of manufacturing a semiconductor devicewhere a glass layer for passivation is formed such that the glass layercovers a pn junction exposure portion in a process of manufacturing amesa semiconductor device (see patent literature 1, for example). Inmanufacturing a semiconductor device which exhibits an excellentswitching characteristic (a fast recovery diode) by using such a methodof manufacturing a semiconductor device, the following manufacturingmethod is adopted. Hereinafter, such a manufacturing method is referredto as “conventional method of manufacturing a semiconductor device”.

FIG. 16 (a) to FIG. 16 (d) and FIG. 17( a) to FIG. 17( d) are views forexplaining such a conventional method of manufacturing a semiconductordevice. FIG. 16( a) to FIG. 16( d) and FIG. 17( a) to FIG. 17( d) areviews showing respective steps of the conventional method.

The conventional method of manufacturing a semiconductor deviceincludes, as shown in FIG. 16 (a) to FIG. 16 (d) and FIG. 17( a) to FIG.17( d), “semiconductor base body forming step”, “trench forming step”,“heavy metal diffusion step”, “glass layer forming step”, “glassprotection film forming step”, “oxide film removing step”, “electrodeforming step”, and “semiconductor base body cutting step” in this order.Hereinafter, the conventional method of manufacturing a semiconductordevice is explained in the order of these steps. In this specification,a main surface of the semiconductor base body on a side where trenchesare formed is referred to a first main surface, and a main surface ofthe semiconductor base body on a side opposite to the first main surfaceis referred to as a second main surface.

(a) Semiconductor base body forming step

Firstly, an n⁺ type semiconductor layer 914 is formed by diffusion of ann type impurity from a surface of an n⁻ type semiconductor layer (n⁻type silicon substrate) 910 on a second main surface side, and a p⁺ typesemiconductor layer 912 is formed by diffusion of a p type impurity froma surface of the n⁻ type semiconductor layer 910 on a first main surfaceside thus forming a semiconductor base body in which a pn junctionarranged parallel to a main surface of the semiconductor base body isformed. It may be possible that an n⁻ type semiconductor layer (n⁻ typeepitaxial layer) is formed on an n⁺ type semiconductor layer (n⁺ typesilicon substrate) and, thereafter, a p⁺ type semiconductor layer isformed by diffusion of a p type impurity from a surface of the n⁻ typesemiconductor layer (n⁻ type epitaxial layer) thus forming asemiconductor base body in which a pn junction arranged parallel to amain surface of the semiconductor base body is formed. Thereafter, oxidefilms 916, 918 are formed by thermal oxidation on a surface of the p⁺type semiconductor layer 912 and a surface of the n⁺ type semiconductorlayer 914 respectively (see FIG. 16( a)).

(b) Trench forming step

Next, predetermined opening portions are formed on the oxide film 916 atpredetermined positions by photo etching. After etching the oxide film,subsequently, the semiconductor base body is etched thus formingtrenches 920 having a depth exceeding the pn junction from the surfaceof the semiconductor base body on the first main surface side (in thiscase, the trenches 920 having a depth exceeding a boundary surfacebetween the n⁻ type semiconductor layer 910 and the n⁺ typesemiconductor layer 914) (see FIG. 16 (b)). Along with such formation ofthe trenches, a pn junction exposure portion A is formed on an innersurfaces of the trench.

(c) Heavy metal diffusion step

Next, a layer 922 which constitutes a heavy metal diffusion source isformed on a surface of the semiconductor base body on a second mainsurface side in such a manner that the oxide film 918 is removed fromthe surface of the semiconductor base body on the second main surfaceside and, thereafter, the layer made of heavy metal (Pt, for example) isformed on the surface of the semiconductor base body on the second mainsurface side by a sputtering method or by resolving heavy metal (Pt, forexample) in solution and applying the solution to the surface of thesemiconductor base body on the second main surface side by spinning.Thereafter, heavy metal is thermally diffused at a predeterminedtemperature so that the carrier recoupling center is formed in theinside of the semiconductor base body (see FIG. 16( c)). The heavy metaldiffusion step may be performed prior to the above-mentioned trenchforming step.

(d) Glass Layer Forming Step

Next, after removing the layer 922 which constitutes the heavy metaldiffusion source, a layer made of the glass composition for protecting asemiconductor junction is formed on an inner surfaces of the trench 920and a surface of the semiconductor base body in the vicinity of thetrench 920 by an electrophoresis method, and the layer made of the glasscomposition for protecting a semiconductor junction is baked so that aglass layer 926 for passivation is formed on a surface of the trench 920(see FIG. 16( d)). Here, an oxide film 924 is formed on a surface of thesemiconductor base body on a second main surface side.

(e) Glass Protection Film Forming Step

Next, a glass protection film (a glass protection film made of apitch-based wax, for example) 928 is formed such that the glassprotection film 928 covers a surface of the glass layer 926 (see FIG.17( a)).

(f) Oxide film removing step

Next, the oxide film 916 is etched using the glass protection film 928as a mask so that the oxide film 916 in an electrode forming region 930and the oxide film 924 formed on the surface of the semiconductor basebody on the second main surface side are removed (see FIG. 17( b)).

(g) Electrode Forming Step

Next, a Ni plating is applied to the semiconductor base body thusforming an anode electrode 932 in the electrode forming region 930 onthe surface of the semiconductor base body on the first main surfaceside and forming a cathode electrode 934 on the surface of thesemiconductor base body on the second main surface side (see FIG. 17(c)). The anode electrode and the cathode electrode may be formed by agas phase method such as vapor deposition or sputtering in place of Niplating.

(h) Semiconductor Base Body Cutting Step

Next, the semiconductor base body is cut by dicing or the like at acenter portion of the glass layer 926 thus dividing the semiconductorbase body into a plurality of chips whereby mesa semiconductor devices(pn diodes) 900 are manufactured (see FIG. 17( d)).

As has been explained heretofore, the conventional method ofmanufacturing a semiconductor device includes the step of forming thetrenches 920 exceeding the pn junction on the surface of thesemiconductor base body from the first main surface side where the pnjunction arranged parallel to the main surface is formed (see FIG. 16(a) and FIG. 16( b)), and the step of forming the glass layer 926 forpassivation in the inside of the trench 920 such that the glass layer926 covers a pn junction exposure portion (see FIG. 16( d)).Accordingly, in the conventional method of manufacturing a semiconductordevice, by cutting the semiconductor base body after forming the glasslayer 926 for passivation in the inside of the trench 920, mesasemiconductor devices having high reliability can be manufactured.

The conventional method of manufacturing a semiconductor device alsoincludes a step of forming the carrier recoupling center in the insideof the semiconductor base body by thermally diffusing heavy metal fromthe surface of the semiconductor base body on the second main surfaceside (see FIG. 16( c)). Accordingly, the conventional method ofmanufacturing a semiconductor device can manufacture a semiconductordevice which exhibits the excellent switching characteristic with ashort reverse recovery time trr.

PRIOR ART LITERATURE Patent Literature

[Patent literature 1] JP-A-2004-87955

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

A glass material which is used in forming a glass layer for passivationis required to satisfy following conditions (a) to (d), that is, thecondition (a) that the glass material can be baked at a propertemperature, the condition (b) that the glass material withstandschemicals used in steps, the condition (c) that the glass material hasexcellent insulation property and the condition (d) that the glassmaterial does not deteriorate characteristics of the semiconductordevice. In view of the above, “a glass material containing lead silicateas a main component” has been widely used conventionally.

However, “the glass material containing lead silicate as a maincomponent” contains lead which imposes a heavy burden on an environmentand hence, it is thought that the use of “the glass material containinglead silicate as a main component” will be prohibited in the nearfuture.

Such circumstances exist not only in a method of manufacturing asemiconductor device for manufacturing a mesa semiconductor device butalso in a method of manufacturing a semiconductor device having highreliability in general where a glass layer for passivation is formed soas to cover a pn junction exposure portion including a method ofmanufacturing a semiconductor device for manufacturing a planar-typesemiconductor device.

The present invention has been made in view of such circumstances, andit is an object of the present invention to provide a glass compositionfor protecting a semiconductor junction, a method of manufacturing asemiconductor device and such a semiconductor device which canmanufacture a semiconductor device having high reliability using a glassmaterial containing no lead in the same manner as a conventional casewhere “a glass material containing lead silicate as a main component” isused.

Means for Solving the Task

[1] The present invention is directed to a glass composition forprotecting a semiconductor junction used in forming a glass layer whichprotects a pn junction in a semiconductor element having a pn junctionexposure portion where the pn junction is exposed, wherein the glasscomposition for protecting a semiconductor junction is made of fineglass particles prepared from a material in a molten state obtained bymelting a glass raw material which contains at least ZnO, SiO₂, B₂O₃,Al₂O₃ and at least two oxides of alkaline earth metals selected from agroup consisting of BaO, CaO and MgO with the following contents andsubstantially contains none of Pb, As, Sb, Li, Na and K, the glasscomposition for protecting a semiconductor junction containing nofiller.

ZnO: 30 mol % to 60 mol %

SiO₂: 5 mol % to 45 mol %

B₂O₃: 5 mol % to 30 mol %

Al₂O₃: 5 mol % to 13 mol %

oxide of alkaline earth metal: 1 mol % to 10 mol %

[2] In the glass composition for protecting a semiconductor junctionaccording to the present invention, it is preferable that the glass rawmaterial substantially contain no Bi.

[3] In the glass composition for protecting a semiconductor junctionaccording to the present invention, it is preferable that the glass rawmaterial substantially contain no P.

[4] In the glass composition for protecting a semiconductor junctionaccording to the present invention, it is preferable that the glass rawmaterial further contain nickel oxide.

[5] In the glass composition for protecting a semiconductor junctionaccording to the present invention, it is preferable that the glass rawmaterial further contain ZrO₂.

[6] In the glass composition for protecting a semiconductor junctionaccording to the present invention, it is preferable that the glasslayer be a glass layer which is formed such that the glass layer coversthe pn junction exposure portion with an insulation layer interposedtherebetween.

[7] In the glass composition for protecting a semiconductor junctionaccording to the present invention, it is preferable that a glasstransition temperature Tg fall within a range of from 540° C. to 680° C.

[8] In the glass composition for protecting a semiconductor junctionaccording to the present invention, it is preferable that an averagelinear expansion coefficient within a temperature range of from 50° C.to 500° C. fall within a range of from 4.5×10⁻⁶ to 5.8×10⁻⁶.

[9] In the glass composition for protecting a semiconductor junctionaccording to the present invention, it is preferable that the content ofZnO fall within a range of from 40 mol % to 56 mol %, the content ofSiO₂ fall within a range of from 8 mol % to 20 mol %, the content ofB₂O₃ fall within a range of from 20 mol % to 30 mol %, the content ofAl₂O₃ fall within a range of from 6 mol % to 10 mol %, and the contentof the oxide of an alkaline earth metal fall within a range of from 2mol % to 5 mol %.

[10] In the glass composition for protecting a semiconductor junctionaccording to the present invention, it is preferable that thesemiconductor element be a semiconductor element made of Si.

[11] In the glass composition for protecting a semiconductor junctionaccording to the present invention, it is preferable that thesemiconductor element be a fast recovery diode.

[12] In the glass composition for protecting a semiconductor junctionaccording to the present invention, it is preferable that thesemiconductor element be a semiconductor element made of SiC.

[13] In the glass composition for protecting a semiconductor junctionaccording to the present invention, it is preferable that thesemiconductor element be a semiconductor element made of GaN.

[14] The present invention is also directed to a method of manufacturinga semiconductor device including, in the following order: a first stepof preparing a semiconductor element having a pn junction exposureportion where a pn junction is exposed; and a second step of forming aglass layer such that the glass layer covers the pn junction exposureportion, wherein in the second step, the glass layer is formed using aglass composition for protecting a semiconductor junction made of fineglass particles prepared from a material in a molten state obtained bymelting a glass raw material which contains at least ZnO, SiO₂, B₂O₃,Al₂O₃ and at least two oxides of alkaline earth metals selected from agroup consisting of BaO, CaO and MgO with the following contents andsubstantially contains none of Pb, As, Sb, Li, Na and K, the glasscomposition for protecting a semiconductor junction containing nofiller.

ZnO: 30 mol % to 60 mol %

SiO₂: 5 mol % to 45 mol %

B₂O₃: 5 mol % to 30 mol %

Al₂O₃: 5 mol % to 13 mol %

oxide of alkaline earth metal: 1 mol % to 10 mol %

[15] In the method of manufacturing a semiconductor device according tothe present invention, it is preferable that the second step include astep of forming an insulation film on the pn junction exposure portion,and a step of forming the glass layer such that the glass layer coversthe pn junction exposure portion with the insulation film interposedtherebetween.

[16] The present invention is also directed to a semiconductor deviceincluding: a semiconductor element having a pn junction exposure portionwhere a pn junction is exposed; and a glass layer which is formed suchthat the glass layer covers the pn junction exposure portion, whereinthe glass layer is formed using a glass composition for protecting asemiconductor junction made of fine glass particles prepared from amaterial in a molten state obtained by melting a glass raw materialwhich contains at least ZnO, SiO₂, B₂O₃, Al₂O₃ and at least two oxidesof alkaline earth metals selected from a group consisting of BaO, CaOand MgO with the following contents and substantially contains none ofPb, As, Sb, Li, Na and K, the glass composition for protecting asemiconductor junction containing no filler.

ZnO: 30 mol % to 60 mol %

SiO₂: 5 mol % to 45 mol %

B₂O₃: 5 mol % to 30 mol %

Al₂O₃: 5 mol % to 13 mol %

oxide of alkaline earth metal: 1 mol % to 10 mol %

[17] In the semiconductor device according to the present invention, itis preferable that the glass layer be formed such that the glass layercovers the pn junction exposure portion with an insulation layerinterposed therebetween.

Advantage of the Invention

According to the glass composition for protecting a semiconductorjunction, the method of manufacturing a semiconductor device and thesemiconductor device of the present invention, as can be clearlyunderstood from examples described later, a semiconductor device havinghigh reliability can be manufactured by using a glass material whichcontains no lead in the same manner as the conventional case where “aglass material containing lead silicate as a main component” is used.

According to the glass composition for protecting a semiconductorjunction, the method of manufacturing a semiconductor device and thesemiconductor device of the present invention, the glass layer is formedby baking the layer made of the glass composition for protecting asemiconductor junction which is made of fine glass particles preparedfrom a material in a molten state obtained by melting a glass rawmaterial which contains at least ZnO, SiO₂, B₂O₃, Al₂O₃ and at least twooxides of alkaline earth metals selected from a group consisting of BaO,CaO and MgO with the previously-mentioned contents, and substantiallycontains none of Pb, As, Sb, Li, Na and K. Due to such composition, aglass transition temperature Tg of the glass composition for protectingthe semiconductor junction of the present invention is low, that is,540° C. to 680° C. Accordingly, as can be clearly understood fromexamples described later, a baking temperature at which a layer made ofthe glass composition for protecting a semiconductor junction of thepresent invention is baked can be set further lower than a bakingtemperature at which a layer made of a conventional “glass materialcontaining lead silicate as a main component” is baked. For example, thebaking temperature at which a layer made of the glass composition forprotecting a semiconductor junction is baked can be set to 600° C. to730° C.

As a result, according to the glass composition for protecting asemiconductor junction, the method of manufacturing a semiconductordevice and the semiconductor device of the present invention, even inthe manufacture of the semiconductor device where the carrier recouplingcenter is decreased by annealing in the manufacturing step of thesemiconductor element (in the step of baking the glass composition forprotecting a semiconductor junction) so that switching characteristic isliable to deteriorate (a fast recovery diode whose reverse recovery timetrr is liable to be prolonged, for example), the switchingcharacteristic hardly deteriorates in the manufacturing step of thesemiconductor element (in the step of baking the glass composition forprotecting a semiconductor junction) thus enabling the manufacture ofthe semiconductor device having excellent switching characteristic.

As a result, according to the glass composition for protecting asemiconductor junction, the method of manufacturing a semiconductordevice and the semiconductor device of the present invention, in themanufacturing step of the semiconductor element (step of baking theglass composition for protecting a semiconductor junction), the glasslayer is hardly crystallized thus enabling the manufacture of thesemiconductor device having a low reverse leakage current IR. In thiscase, it is possible to manufacture a semiconductor device having a lowreverse leakage current IR in a stable manner even when a backgroundoxide film is not formed between the semiconductor base body and theglass layer (see embodiment 4 and examples 2 to 6 described later).

When the glass composition for protecting a semiconductor junctioncontaining a filler is used as the glass composition for protecting asemiconductor junction, there is a case where at the time of forming alayer made of the glass composition for protecting a semiconductorjunction such that the layer covers the pn junction, it is difficult touniformly form the layer made of the glass composition for protecting asemiconductor junction. That is, when a layer made of the glasscomposition for protecting a semiconductor junction is formed by anelectrophoresis method, it is difficult to uniformly form the layer madeof the glass composition for protecting a semiconductor junction due tonon-uniform electrophoresis. On the other hand, when a layer made of theglass composition for protecting a semiconductor junction is formed by aspin coating method, a screen printing method or a doctor blade method,there is a case where it is difficult to uniformly form a layer made ofthe glass composition for protecting a semiconductor junction due todifference in particle size, specific gravity or the like.

To the contrary, according to the glass composition for protecting asemiconductor junction, the method of manufacturing a semiconductordevice and the semiconductor device of the present invention, the layermade of the glass composition for protecting a semiconductor junctionwhich contains no filler is used as the glass composition for protectinga semiconductor junction and hence, in forming the layer made of theglass composition for protecting a semiconductor junction such that thelayer covers the pn junction, it is possible to uniformly form the layermade of the glass composition for protecting a semiconductor junction.

In the glass composition for protecting a semiconductor junction, themethod of manufacturing a semiconductor device and the semiconductordevice of the present invention, “to contain at least some specificcomponents (ZnO, SiO₂ and the like)” means not only the case where theglass composition contains only some specific components but also thecase where the glass composition also contains other components whichcan be usually contained in the glass composition besides some specificcomponents.

In the glass composition for protecting a semiconductor junction, themethod of manufacturing a semiconductor device and the semiconductordevice of the present invention, “to substantially contain no specificelement (Pb, As or the like)” means that the glass composition containsno any such specific element as the component of the glass composition,and does not exclude the glass composition in which the above-mentionedspecific element is mixed as an unavoidable impurity in the glassmaterials which constitute respective components of glass.

In the glass composition for protecting a semiconductor junction, themethod of manufacturing a semiconductor device and the semiconductordevice of the present invention, “to contain no specific element (Pb, Asor the like)” means that the glass composition contains neither an oxideof the specific element nor a nitride or the like of the specificelement.

The reason that the glass composition substantially contains no Pb isthat the object of the present invention lies in that a semiconductordevice having high reliability can be manufactured by using a glassmaterial which contains no lead in the same manner as the conventionalcase where “a glass material containing lead silicate as a maincomponent” is used.

The reason that the glass composition substantially contains neither Asnor Sb is that these components are toxic and hence, there has been themovement to limit the use of these components.

The reason that the glass composition substantially contains none of Li,Na and K is that when the glass composition contains these components,although the glass composition can acquire advantageous effects withrespect to an average linear expansion coefficient and a bakingtemperature, there is a case where the insulation property of the glasscomposition deteriorates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A, FIG. 1B, FIG. 1C, and FIG. 1D are views for explaining a methodof manufacturing a semiconductor device according to an embodiment 4.

FIG. 2A, FIG. 2B, FIG. 2C, and FIG. 2D are views for explaining themethod of manufacturing a semiconductor device according to theembodiment 4.

FIG. 3A, FIG. 3B, FIG. 3C, and FIG. 3D are views for explaining a methodof manufacturing a semiconductor device according to an embodiment 5.

FIG. 4A, FIG. 4B, FIG. 4C, and FIG. 4D are views for explaining themethod of manufacturing a semiconductor device according to theembodiment 5.

FIG. 5A, FIG. 5B, FIG. 5C, and FIG. 5D are views for explaining a methodof manufacturing a semiconductor device according to an embodiment 6.

FIG. 6A, FIG. 6B, and FIG. 6C are views for explaining the method ofmanufacturing a semiconductor device according to the embodiment 6.

FIG. 7A, FIG. 7B, and FIG. 7C are views for explaining a method ofmanufacturing a semiconductor device according to an embodiment 7.

FIG. 8A, FIG. 8B, and FIG. 8C are views for explaining the method ofmanufacturing a semiconductor device according to the embodiment 7.

FIG. 9A, FIG. 9B, and FIG. 9C are views for explaining the method ofmanufacturing a semiconductor device according to the embodiment 7.

FIG. 10A, FIG. 10B, and FIG. 10C are views for explaining the method ofmanufacturing a semiconductor device according to the embodiment 7.

FIG. 11 is a table showing conditions and results of examples.

FIG. 12A and FIG. 12B are views for explaining bubbles b generated inthe inside of a glass layer 126 in a preliminary evaluation.

FIG. 13A and FIG. 13B are Photographs for explaining bubbles b generatedin the inside of the glass layer 126 in a subsequent evaluation.

FIG. 14 is a graph showing a reverse current in a semiconductor devicewhich is manufactured using a glass composition for protecting asemiconductor junction according to an example 3.

FIG. 15 is a graph for explaining a method of measuring a reverserecovery time trr.

FIG. 16A, FIG. 16B, FIG. 16C, and FIG. 16D are views for explaining aconventional method of manufacturing a semiconductor device.

FIG. 17A, FIG. 17B, FIG. 17C, and FIG. 17D are views for explaining theconventional method of manufacturing a semiconductor device.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a glass composition for protecting a semiconductorjunction, a method of manufacturing a semiconductor device and such asemiconductor device according to the present invention are explained inconjunction with embodiments shown in the drawings.

Embodiment 1

The embodiment 1 relates to a glass composition for protecting asemiconductor junction. Particularly, the embodiment 1 is the embodimentwhich includes glass compositions for protecting a semiconductorjunction according to examples 3 to 6 described later.

The glass composition for protecting a semiconductor junction accordingto the embodiment 1 is a glass composition for protecting asemiconductor junction used in forming a glass layer which protects a pnjunction in a semiconductor element having a pn junction exposureportion where the pn junction is exposed, wherein the glass compositionfor protecting a semiconductor junction is made of fine glass particlesprepared from a material in a molten state obtained by melting a glassraw material which contains at least ZnO, SiO₂, B₂O₃, Al₂O₃, at leasttwo oxides of alkaline earth metals selected from a group consisting ofBaO, CaO and MgO, ZrO₂ and nickel oxide with the following contents andsubstantially contains none of Pb, As, Sb, Li, Na and K, the glasscomposition for protecting a semiconductor junction containing nofiller.

ZnO: 30 mol % to 60 mol %

SiO₂: 5 mol % to 45 mol %

B₂O₃: 5 mol % to 30 mol %

Al₂O₃: 5 mol % to 13 mol %

oxide of alkaline earth metal: 1 mol % to 10 mol %

ZrO₂: 0.1 mol % to 3.0 mol %

nickel oxide: 0.01 mol % to 2.0 mol %

In the glass composition for protecting a semiconductor junctionaccording to the embodiment 1, the glass raw material may contain, as anoxide of an alkaline earth metal, all of BaO, CaO and MgO, or two oxidesout of BaO, CaO and MgO (BaO and CaO, for example).

In the glass composition for protecting a semiconductor junctionaccording to the embodiment 1, it is preferable that the glass rawmaterial substantially contain none of Bi and P.

In the glass composition for protecting a semiconductor junctionaccording to the embodiment 1, a glass transition temperature Tg fallswithin a range of from 540° C. to 680° C. Further, in the glasscomposition for protecting a semiconductor junction according to theembodiment 1, an average linear expansion coefficient within atemperature range of from 50° C. to 500° C. falls within a range of from4.5×10⁻⁶ to 5.8×10⁻⁶.

According to the glass composition for protecting a semiconductorjunction according to the embodiment 1, as can be clearly understoodfrom examples described later, a semiconductor device having highreliability can be manufactured by using a glass material which containsno lead in the same manner as the conventional case where “a glassmaterial containing lead silicate as a main component” is used.

The glass composition for protecting a semiconductor junction accordingto the embodiment 1 is the glass composition for protecting asemiconductor junction which is made of fine glass particles preparedfrom a material in a molten state obtained by melting a glass rawmaterial which contains at least ZnO, SiO₂, B₂O₃, Al₂O₃ and at least twooxides of alkaline earth metals selected from a group consisting of BaO,CaO and MgO with the previously-mentioned contents, and substantiallycontains none of Pb, As, Sb, Li, Na and K. Due to such composition, aglass transition temperature Tg of the glass composition for protectingthe semiconductor junction according to the embodiment 1 is low, thatis, 540° C. to 680° C. Accordingly, as can be clearly understood fromexamples described later, a baking temperature at which a layer made ofthe glass composition for protecting a semiconductor junction accordingto the embodiment 1 is baked can be set further lower than a bakingtemperature at which a layer made of a conventional “glass materialcontaining lead silicate as a main component” is baked. For example, thebaking temperature at which a layer made of the glass composition forprotecting a semiconductor junction is baked can be set to 600° C. to730° C.

As a result, according to the glass composition for protecting asemiconductor junction according to the embodiment 1, even in themanufacture of the semiconductor device where the carrier recouplingcenter is decreased by annealing in the manufacturing step of thesemiconductor element (in the step of baking the glass composition forprotecting a semiconductor junction) so that switching characteristic isliable to deteriorate (a fast recovery diode whose reverse recovery timetrr is liable to be prolonged, for example), the switchingcharacteristic hardly deteriorates in the manufacturing step of thesemiconductor element (in the step of baking the glass composition forprotecting a semiconductor junction) thus enabling the manufacture ofthe semiconductor device having excellent switching characteristic.

According to the glass composition for protecting a semiconductorjunction according to the embodiment 1, in the manufacturing step of thesemiconductor element (step of baking the glass composition forprotecting a semiconductor junction), the glass layer is hardlycrystallized thus enabling the manufacture of the semiconductor devicehaving a low reverse leakage current IR. Accordingly, it becomespossible to manufacture a semiconductor device having a low reverseleakage current IR in a stable manner even when a background oxide filmis not formed between a semiconductor base body and the glass layer (seeembodiment 4 and examples 3 to 6 described later).

According to the glass composition for protecting a semiconductorjunction according to the embodiment 1, the layer made of the glasscomposition for protecting a semiconductor junction which contains nofiller is used as the glass composition for protecting a semiconductorjunction and hence, in forming the layer made of the glass compositionfor protecting a semiconductor junction such that the layer covers thepn junction, it is possible to uniformly form the layer made of theglass composition for protecting a semiconductor junction.

Among the glass compositions for protecting a semiconductor junctionaccording to the embodiment 1, in the case of the glass compositions forprotecting a semiconductor junction including glass compositions forprotecting a semiconductor junction of examples 3, 4 and 6 describedlater, that is, the glass compositions for protecting a semiconductorjunction where the content of ZnO falls within a range of from 40 mol %to 56 mol %, the content of SiO₂ falls within a range of from 8 mol % to20 mol %, the content of B₂O₃ falls within a range of from 20 mol % to30 mol %, the content of Al₂O₃ falls within a range of from 6 mol % to10 mol %, and the content of an oxide of an alkaline earth metal fallswithin a range of from 2 mol % to 5 mol %, the glass transitiontemperature Tg can be further lowered, that is, 540° C. to 620° C. Ascan be clearly understood from examples described later, a bakingtemperature at which a layer made of the glass composition forprotecting a semiconductor junction according to the embodiment 1 isbaked can be set further lower than a baking temperature at which alayer made of a conventional “glass material containing lead silicate asa main component” is baked. For example, the baking temperature at whicha layer made of the glass composition for protecting a semiconductorjunction is baked can be set to 600° C. to 730° C.

According to the glass composition for protecting a semiconductorjunction according to the embodiment 1, it is possible to set an averagelinear expansion coefficient of the glass composition for protecting asemiconductor junction within a temperature range of from 50° C. to 500°C. to a value (4.8×10⁻⁶ to 5.8×10⁻⁶, for example) close to a linearexpansion coefficient of a semiconductor material (Si, SiC, GaN) (Si:3.7×10⁻⁶, SiC: 4.4×10⁻⁶, GaN: 5.6×10⁻⁶). Accordingly, the warping of awafer during steps is decreased and hence, a semiconductor device havingan excellent forward characteristic can be manufactured using a thinwafer, while a semiconductor device having an excellent reversecharacteristic can be manufactured by increasing a thickness of a glasslayer.

The reason the content of ZnO is set to a value which falls within arange of from 30 mol % to 60 mol % is that when the content of ZnO isless than 30 mol %, there is a tendency that a baking temperature needsto be elevated, while when the content of ZnO exceeds 60 mol %, there isa case where the chemical resistance deteriorates or the insulationproperty is degraded and, further, there is a tendency that the glasscomposition is liable to be crystallized in the process ofvitrification.

The reason the content of SiO₂ is set to a value which falls within arange of from 5 mol % to 45 mol % is that when the content of SiO₂ isless than 5 mol %, there is a case where the chemical resistancedeteriorates or the insulation property is degraded, while when thecontent of SiO₂ exceeds 45 mol %, there is a tendency that a bakingtemperature needs to be elevated.

The reason the content of B₂O₃ is set to a value which falls within arange of from 5 mol % to 30 mol % is that when the content of B₂O₃ isless than 5 mol %, there is a tendency that a baking temperature needsto be elevated, while when the content of B₂O₃ exceeds 30 mol %, thereis a tendency that an average linear expansion coefficient is increased.

The reason the content of Al₂O₃ is set to a value which falls within arange of from 5 mol % to 13 mol % is that when the content of Al₂O₃ isless than 5 mol %, there is a tendency that the glass composition isliable to be crystallized in the process of vitrification, while whenthe content of Al₂O₃ exceeds 13 mol %, there is a tendency that theinsulation property is degraded.

The reason the content of an oxide of an alkaline earth metal is set toa value which falls within a range of from 1 mol % to 10 mol % is thatwhen the content of an oxide of an alkaline earth metal is less than 1mol %, there is a tendency that a baking temperature needs to beelevated, while when the content of an oxide of an alkaline earth metalexceeds 10 mol %, there is a case where the chemical resistancedeteriorates or the insulation property is degraded.

The reason the glass composition contains at least two oxides of analkaline earth metal as oxides of an alkaline earth metal in thisembodiment is that it is possible to lower a baking temperature bymaking use of an alkali mixing effect (effect that vitrification isfacilitated by allowing the composition to contain a plurality of atomshaving different atomic radii).

The reason the content of ZrO₂ is set to a value which falls within arange of from 0.1 mol % to 3.0 mol % is that when the content of ZrO₂ isless than 0.1 mol %, there is a case where the chemical resistancedeteriorates or the insulation property is degraded, while when thecontent of ZrO₂ exceeds 3.0 mol %, a melting temperature of glass isincreased.

The reason the content of nickel oxide is set to a value which fallswithin a range of from 0.01 mol % to 2.0 mol % is that when the contentof nickel oxide is less than 0.01 mol %, there is a case where itbecomes difficult to suppress the generation of bubbles which may begenerated from a boundary surface between a “layer made of the glasscomposition for protecting a semiconductor junction” and a semiconductorsubstrate in step of baking the “layer made of the glass composition forprotecting a semiconductor junction”, while when the content of nickeloxide exceeds 2.0 mol %, there is a tendency that the glass compositionis liable to be crystallized in the process of vitrification.

The glass composition for protecting a semiconductor junction accordingto the embodiment 1 can be manufactured as follows. That is, glass rawmaterials (ZnO, SiO₂, H₃BO₃, Al₂O₃, BaCO₃, CaCO₃, MgO, ZrO₂ and NiO) areprepared at the above-mentioned composition ratio (molar ratio), theseglass raw materials are sufficiently mixed and stirred by a mixer and,thereafter, the mixed glass raw material is put into a platinumcrucible, and is melted for a predetermined time at a predeterminedtemperature (1250° C. to 1350° C., for example) in an electric furnace.Then, the material in a molten state is made to flow out from thecrucible and is fed to water-cooled rolls so that glass flakes in aflaky shape are obtained. Thereafter, the glass flakes are pulverized bya ball mill or the like until the glass flakes obtain a predeterminedaverage particle size thus obtaining the powdery glass composition.

The glass composition for protecting a semiconductor junction accordingto the embodiment 1 is preferably applicable to any one of asemiconductor element made of Si, a semiconductor element made of SiCand a semiconductor element made of GaN.

The glass composition for protecting a semiconductor junction accordingto the embodiment 1 is preferably applicable to a semiconductor devicewhere a carrier recoupling center is decreased by annealing in themanufacturing step of the semiconductor element (in the step of baking aglass composition for protecting a semiconductor junction) so that aswitching characteristic is liable to deteriorate (fast recovery diodewhose reverse recovery time trr is liable to be prolonged, for example).

Further, in the glass composition for protecting a semiconductorjunction according to the embodiment 1, an average linear expansioncoefficient within a temperature range of from 50° C. to 500° C. fallswithin a range of from 4.5×10⁻⁶ to 5.8×10⁻⁶ and hence, the glasscomposition for protecting a semiconductor junction according to theembodiment 1 is also preferably applicable to a semiconductor elementmade of SiC whose average linear expansion coefficient is relativelyhigh (linear expansion coefficient of SiC: 4.4×10⁻⁶) or a semiconductorelement made of GaN whose average linear expansion coefficient isrelatively high (linear expansion coefficient of GaN: 5.6×10⁻⁶).

Embodiment 2

The embodiment 2 relates to a glass composition for protecting asemiconductor junction. Particularly, the embodiment 2 relates to aglass composition for protecting a semiconductor junction according toan example 1 described later.

The glass composition for protecting a semiconductor junction accordingto the embodiment 2 basically contains the substantially same componentsas the glass composition for protecting a semiconductor junctionaccording to the embodiment 1. However, the glass composition forprotecting a semiconductor junction according to the embodiment 2differs from the glass composition for protecting a semiconductorjunction according to the embodiment 1 with respect to a point that theglass composition for protecting a semiconductor junction according tothe embodiment 2 contains no nickel oxide. That is, the glasscomposition for protecting a semiconductor junction according to theembodiment 2 which basically contains the substantially same componentsas the glass composition for protecting a semiconductor junctionaccording to the embodiment 1 is the glass composition for protecting asemiconductor junction made of fine glass particles prepared from amaterial in a molten state obtained by melting a glass raw materialwhich contains at least ZnO, SiO₂, B₂O₃, Al₂O₃, at least two oxides ofalkaline earth metals selected from a group consisting of BaO, CaO andMgO and ZrO₂, and substantially contains none of Pb, As, Sb, Li, Na andK. Further, the glass composition for protecting a semiconductorjunction contains no filler.

With respect to the content of ZnO, the content of SiO₂, the content ofB₂O₃, the content of Al₂O₃, the content of an oxide of an alkaline earthmetal and the content of ZrO₂, the glass composition for protecting asemiconductor junction according to the embodiment 2 has the samecontents as the glass composition for protecting a semiconductorjunction according to the embodiment 1.

Further, in the glass composition for protecting a semiconductorjunction according to the embodiment 2, in the substantially same manneras the glass composition for protecting a semiconductor junctionaccording to the embodiment 1, a glass transition temperature Tg fallswithin a range of from 540° C. to 680° C., and an average linearexpansion coefficient within a temperature range of from 50° C. to 500°C. falls within a range of from 4.5×10⁻⁶ to 5.8×10⁻⁶.

In this manner, the glass composition for protecting a semiconductorjunction according to the embodiment 2 differs from the glasscomposition for protecting a semiconductor junction according to theembodiment 1 with respect to a point that the glass composition forprotecting a semiconductor junction according to the embodiment 2contains no nickel oxide. However, in the same manner as the glasscomposition for protecting a semiconductor junction according to theembodiment 1, according to the glass composition for protecting asemiconductor junction according to the embodiment 2, a semiconductordevice having high reliability can be manufactured by using a glassmaterial which contains no lead in the same manner as the conventionalcase where “a glass material containing lead silicate as a maincomponent” is used.

Further, with respect to the content of ZnO, the content of SiO₂, thecontent of B₂O₃, the content of Al₂O₃, the content of an oxide of analkaline earth metal and the content of ZrO₂, the glass composition forprotecting a semiconductor junction according to the embodiment 2 hasthe same contents as the glass composition for protecting asemiconductor junction according to the embodiment 1. Accordingly, inthe same manner as the glass composition for protecting a semiconductorjunction according to the embodiment 1, a glass transition temperatureTg of the glass composition for protecting the semiconductor junctionaccording to the embodiment 2 is low, that is, 540° C. to 680° C. andhence, as can be clearly understood from examples described later, abaking temperature at which a layer made of the glass composition forprotecting a semiconductor junction according to the embodiment 2 isbaked can be set further lower than a baking temperature at which alayer made of a conventional “glass material containing lead silicate asa main component” is baked. For example, the baking temperature at whicha layer made of the glass composition for protecting a semiconductorjunction is baked can be set to 600° C. to 730° C.

As a result, according to the glass composition for protecting asemiconductor junction according to the embodiment 2, in the same manneras the glass composition for protecting a semiconductor junctionaccording to the embodiment 1, even in the manufacture of thesemiconductor device where the carrier recoupling center is decreased byannealing in the manufacturing step of the semiconductor element (in thestep of baking the glass composition for protecting a semiconductorjunction) so that switching characteristic is liable to deteriorate (afast recovery diode whose reverse recovery time trr is liable to beprolonged, for example), the switching characteristic hardlydeteriorates in the manufacturing step of the semiconductor element (inthe step of baking the glass composition for protecting a semiconductorjunction) thus enabling the manufacture of the semiconductor devicehaving an excellent switching characteristic.

As a result, according to the glass composition for protecting asemiconductor junction according to the embodiment 2, in the same manneras the glass composition for protecting a semiconductor junctionaccording to the embodiment 1, in the manufacturing step of thesemiconductor element (step of baking the glass composition forprotecting a semiconductor junction), the glass layer is hardlycrystallized thus enabling the manufacture of the semiconductor devicehaving a low reverse leakage current IR (see embodiments 4 and 5described later).

According to the glass composition for protecting a semiconductorjunction according to the embodiment 2, the layer made of the glasscomposition for protecting a semiconductor junction which contains nofiller is used as the glass composition for protecting a semiconductorjunction and hence, in forming the layer made of the glass compositionfor protecting a semiconductor junction such that the layer covers thepn junction, it is possible to uniformly form the layer made of theglass composition for protecting a semiconductor junction.

The glass composition for protecting a semiconductor junction accordingto the embodiment 2 has the substantially same constitution as the glasscomposition for protecting a semiconductor junction according to theembodiment 1 except for the point that the glass composition forprotecting a semiconductor junction according to the embodiment 2contains no nickel oxide. Accordingly, the glass composition forprotecting a semiconductor junction according to the embodiment also hasadvantageous effects derived from the same constitution out of theadvantageous effects which the glass composition for protecting asemiconductor junction according to the embodiment 1 has.

The reason the content of ZnO, the content of SiO₂, the content of B₂O₃,the content of Al₂O₃, the content of an oxide of an alkaline earth metaland the content of ZrO₂ are set to values which fall within theabove-mentioned ranges is substantially equal to the reason explained inconjunction with the glass composition for protecting a semiconductorjunction according to the embodiment 1.

The reason the glass composition for protecting a semiconductor junctionaccording to the embodiment 2 contains no nickel oxide is that even whenthe glass composition for protecting a semiconductor junction accordingto the embodiment 2 contains no a nickel oxide, there is a case where itis possible to suppress the generation of bubbles which may be generatedfrom a boundary surface between a “layer made of the glass compositionfor protecting a semiconductor junction” and a silicon substrate in stepof baking the “layer made of the glass composition for protecting asemiconductor junction”.

The glass composition for protecting a semiconductor junction accordingto the embodiment 2 can be manufactured as follows. That is, glass rawmaterials (ZnO, SiO₂, H₃BO₃, Al₂O₃, BaCO₃, CaCO₃, MgO and ZrO₂) areprepared at the above-mentioned composition ratio (molar ratio), theseglass raw materials are sufficiently mixed and stirred by a mixer and,thereafter, the mixed glass raw material is put into a platinumcrucible, and is melted for a predetermined time at a predeterminedtemperature (1250° C. to 1350° C., for example) in an electric furnace.Then, the material in a molten state is made to flow out from thecrucible and is fed to water-cooled rolls so that glass flakes in aflaky shape are obtained. Thereafter, the glass flakes are pulverized bya ball mill or the like until the glass flakes obtain a predeterminedaverage particle size thus obtaining the powdery glass composition.

In the same manner as the glass composition for protecting asemiconductor junction according to the embodiment 1, the glasscomposition for protecting a semiconductor junction according to theembodiment 2 is also preferably applicable to any one of a semiconductorelement made of Si, a semiconductor element made of SiC and asemiconductor elements made of GaN.

Embodiment 3

The embodiment 3 relates to a glass composition for protecting asemiconductor junction.

The glass composition for protecting a semiconductor junction accordingto the embodiment 3 basically contains the substantially same componentsas the glass composition for protecting a semiconductor junctionaccording to the embodiment 1. However, the glass composition forprotecting a semiconductor junction according to the embodiment 3differs from the glass composition for protecting a semiconductorjunction according to the embodiment 1 with respect to a point that theglass composition for protecting a semiconductor junction according tothe embodiment 3 contains no ZrO₂. That is, the glass composition forprotecting a semiconductor junction according to the embodiment 3 is theglass composition for protecting a semiconductor junction made of fineglass particles prepared from a material in a molten state obtained bymelting a glass raw material which contains at least ZnO, SiO₂, B₂O₃,Al₂O₃, at least two oxides of alkaline earth metals selected from agroup consisting of BaO, CaO and MgO and nickel oxide, and substantiallycontains none of Pb, As, Sb, Li, Na and K. Further, the glasscomposition for protecting a semiconductor junction contains no filler.

With respect to the glass composition for protecting a semiconductorjunction according to the embodiment 3, the content of ZnO, the contentof SiO₂, the content of B₂O₃, the content of Al₂O₃, the content of anoxide of an alkaline earth metal and the content of nickel oxide areequal to these contents of the glass composition for protecting asemiconductor junction according to the embodiment 1.

Further, in the glass composition for protecting a semiconductorjunction according to the embodiment 3, in the substantially same manneras the glass composition for protecting a semiconductor junctionaccording to the embodiment 1, a glass transition temperature Tg fallswithin a range of from 540° C. to 680° C., and an average linearexpansion coefficient within a temperature range of from 50° C. to 500°C. falls within a range of from 4.5×10⁻⁶ to 5.8×10⁻⁶.

In this manner, the glass composition for protecting a semiconductorjunction according to the embodiment 3 differs from the glasscomposition for protecting a semiconductor junction according to theembodiment 1 with respect to a point that the glass composition forprotecting a semiconductor junction according to the embodiment 3contains no ZrO₂. However, in the same manner as the glass compositionfor protecting a semiconductor junction according to the embodiment 1,according to the glass composition for protecting a semiconductorjunction according to the embodiment 3, a semiconductor device havinghigh reliability can be manufactured by using a glass material whichcontains no lead in the same manner as the conventional case where “aglass material containing lead silicate as a main component” is used.

Further, with respect to the content of ZnO, the content of SiO₂, thecontent of B₂O₃, the content of Al₂O₃, the content of an oxide of analkaline earth metal and the content of ZrO₂, the glass composition forprotecting a semiconductor junction according to the embodiment 2 hasthe same contents as the glass composition for protecting asemiconductor junction according to the embodiment 1. Accordingly, inthe same manner as the glass composition for protecting a semiconductorjunction according to the embodiment 1, a glass transition temperatureTg of the glass composition for protecting the semiconductor junctionaccording to the embodiment 3 is low, that is, 540° C. to 680° C. andhence, as can be clearly understood from examples described later, abaking temperature at which a layer made of the glass composition forprotecting a semiconductor junction according to the embodiment 3 isbaked can be set further lower than a baking temperature at which alayer made of a conventional “glass material containing lead silicate asa main component” is baked. For example, the baking temperature at whicha layer made of the glass composition for protecting a semiconductorjunction is baked can be set to 600° C. to 730° C.

As a result, according to the glass composition for protecting asemiconductor junction according to the embodiment 3, in the same manneras the glass composition for protecting a semiconductor junctionaccording to the embodiment 1, even in the manufacture of thesemiconductor device where the carrier recoupling center is decreased byannealing in the manufacturing step of the semiconductor element (in thestep of baking the glass composition for protecting a semiconductorjunction) so that switching characteristic is liable to deteriorate (afast recovery diode whose reverse recovery time trr is liable to beprolonged, for example), the switching characteristic hardlydeteriorates in the manufacturing step of the semiconductor element (inthe step of baking the glass composition for protecting a semiconductorjunction) thus enabling the manufacture of the semiconductor devicehaving excellent switching characteristic.

In the above-mentioned case, according to the glass composition forprotecting a semiconductor junction according to the embodiment 3, inthe same manner as the glass composition for protecting a semiconductorjunction according to the embodiment 1, in the manufacturing step of thesemiconductor element (step of baking the glass composition forprotecting a semiconductor junction), the glass layer is hardlycrystallized thus enabling the manufacture of the semiconductor devicehaving a low reverse leakage current IR. In this case, it is possible tomanufacture a semiconductor device having a low reverse leakage currentIR in a stable manner even when a background oxide film is not formedbetween the semiconductor base body and the glass layer (see theembodiment 4 and the example 2 described later).

According to the glass composition for protecting a semiconductorjunction according to the embodiment 3, the layer made of the glasscomposition for protecting a semiconductor junction which contains nofiller is used as the glass composition for protecting a semiconductorjunction and hence, in forming the layer made of the glass compositionfor protecting a semiconductor junction such that the layer covers thepn junction, it is possible to uniformly form the layer made of theglass composition for protecting a semiconductor junction.

The glass composition for protecting a semiconductor junction accordingto the embodiment 3 has the substantially same constitution as the glasscomposition for protecting a semiconductor junction according to theembodiment 1 except for the point that the glass composition forprotecting a semiconductor junction according to the embodiment 3contains no ZrO₂. Accordingly, the glass composition for protecting asemiconductor junction according to the embodiment 3 also hasadvantageous effects derived from the same constitution out of theadvantageous effects which the glass composition for protecting asemiconductor junction according to the embodiment 1 has.

The reason the content of ZnO, the content of SiO₂, the content of B₂O₃,the content of Al₂O₃, the content of an oxide of an alkaline earth metaland the content of nickel oxide are set to values which fall within theabove-mentioned ranges is substantially equal to the reason explained inconjunction with the glass composition for protecting a semiconductorjunction according to the embodiment 1.

The reason the glass composition for protecting a semiconductor junctionaccording to the embodiment 3 contains no ZrO₂ is that there is a casewhere the glass composition sufficiently exhibits excellent chemicalresistance even when the glass composition contains no ZrO₂.

The glass composition for protecting a semiconductor junction accordingto the embodiment 3 can be manufactured as follows. That is, glass rawmaterials (ZnO, SiO₂, H₂BO₂, Al₂O₃, BaCO₂, CaCO₃, MgO and NiO) areprepared at the above-mentioned composition ratio (molar ratio), theseglass raw materials are sufficiently mixed and stirred by a mixer and,thereafter, the mixed glass raw material is put into a platinumcrucible, and is melted for a predetermined time at a predeterminedtemperature (1250° C. to 1350° C., for example) in an electric furnace.Then, the material in a molten state is made to flow out from thecrucible and is fed to water-cooled rolls so that glass flakes in aflaky shape are obtained. Thereafter, the glass flakes are pulverized bya ball mill or the like until the glass flakes obtain a predeterminedaverage particle size thus obtaining the powdery glass composition.

In the same manner as the glass composition for protecting asemiconductor junction according to the embodiment 1, the glasscomposition for protecting a semiconductor junction according to theembodiment 3 is also preferably applicable to any one of a semiconductorelement made of Si, a semiconductor element made of SiC and asemiconductor element made of GaN.

Embodiment 4

The embodiment 4 relates to a method of manufacturing a semiconductordevice.

The method of manufacturing a semiconductor device according to theembodiment 4 includes, in the following order: a first step of preparinga semiconductor element which includes a pn junction exposure portionwhere a pn junction is exposed; and a second step of forming a glasslayer such that the glass layer covers the pn junction exposure portion.In the second step, the glass layer is formed using the glasscomposition for protecting a semiconductor junction according to theembodiment 1. The first step includes: a step of preparing asemiconductor base body in which a pn junction arranged parallel to amain surface of the semiconductor base body is formed; and a step offorming trenches having a depth exceeding the pn junction from a surfaceof a semiconductor base body on a first main surface side thus forming apn junction exposure portion in the inside of the trench, and the secondstep includes a step of forming the glass layer such that the glasslayer directly covers the pn junction exposure portion in the inside ofthe trench.

FIG. 1( a) to FIG. 1( d) and FIG. 2( a) to FIG. 2( d) are views forexplaining the method of manufacturing a semiconductor device accordingto the embodiment 4. FIG. 1( a) to FIG. 1( d) and FIG. 2( a) to FIG. 2(d) are views showing respective steps.

The method of manufacturing a semiconductor device according to theembodiment 4 includes, as shown in FIG. 1( a) to FIG. 1( d) and FIG. 2(a) to FIG. 2( d), “semiconductor base body forming step”, “trenchforming step”, “heavy metal diffusion step”, “glass layer forming step”,“glass protection film forming step”, “oxide film removing step”,“electrode forming step” and “semiconductor base body cutting step” inthis order. Hereinafter, the method of manufacturing a semiconductordevice according to the embodiment 4 is explained in the order of thesesteps.

(a) Semiconductor Base Body Forming Step

Firstly, an n⁺ type semiconductor layer 114 is formed by diffusion of ann type impurity from a surface of an n⁻ type semiconductor layer (n⁻type silicon substrate) 110 on a second main surface side, and a p⁺ typesemiconductor layer 112 is formed by diffusion of a p type impurity froma surface of the n⁻ type semiconductor layer 110 on a first main surfaceside thus forming a semiconductor base body in which a pn junctionarranged parallel to a main surface of the semiconductor base body isformed. It may be possible that an n⁻ type semiconductor layer (n⁻ typeepitaxial layer) is formed on an n⁺ type semiconductor layer (n⁺ typesilicon substrate) and, thereafter, a p⁺ type semiconductor layer isformed by diffusion of a p type impurity from a surface of the n⁻ typesemiconductor layer (n⁻ type epitaxial layer) thus forming asemiconductor base body in which a pn junction arranged parallel to amain surface of the semiconductor base body is formed. Thereafter, oxidefilms 116, 118 are formed by thermal oxidation on a surface of the p⁺type semiconductor layer 112 and a surface of the n⁺ type semiconductorlayer 114 respectively (see FIG. 1( a)).

(b) Trench Forming Step

Next, predetermined opening portions are formed on the oxide film 116 atpredetermined positions by photo etching.

After etching the oxide film, subsequently, the semiconductor base bodyis etched thus forming trenches 120 having a depth exceeding the pnjunction from the surface of the semiconductor base body on the firstmain surface side (in this case, the trenches 120 having a depthexceeding a boundary surface between the n⁻ type semiconductor layer 110and the n⁺ type semiconductor layer 114) (see FIG. 1( b)). Along withsuch formation of the trenches, a pn junction exposure portion A isformed on an inner surfaces of the trench.

(c) Heavy Metal Diffusion Step

Next, a layer 122 which constitutes a heavy metal diffusion source isformed on a surface of the semiconductor base body on a second mainsurface side in such a manner that the oxide film 118 is removed fromthe surface of the semiconductor base body on the second main surfaceside and, thereafter, the layer made of heavy metal (Pt, for example) isformed on the surface of the semiconductor base body on the second mainsurface side by a sputtering method or by resolving heavy metal (Pt, forexample) in solution and applying the solution to the surface of thesemiconductor base body on the second main surface side by spinning.Thereafter, heavy metal is thermally diffused at a predeterminedtemperature so that the carrier recoupling center is formed in theinside of the semiconductor base body (see FIG. 1( c)). The heavy metaldiffusion step may be performed prior to the above-mentioned trenchforming step.

(d) Glass Layer Forming Step

Next, after removing the layer 122 which constitutes the heavy metaldiffusion source, a layer made of the glass composition for protecting asemiconductor junction is formed on an inner surfaces of the trench 120and a surface of the semiconductor base body in the vicinity of thetrench 120 by an electrophoresis method, and the layer made of the glasscomposition for protecting a semiconductor junction is baked so that aglass layer 126 for passivation is formed on a surface of the trench 120(see FIG. 1( d)). Accordingly, the pn junction exposure portion A in theinside of the trench 120 is brought into a state where the pn junctionexposure portion A is directly covered with the glass layer 126. Whenthe layer made of the glass composition for protecting a semiconductorjunction is baked, an oxide film 124 is formed on a second main surfaceside of the semiconductor base body.

(e) Glass Protection Film Forming Step

Next, a glass protection film (a glass protection film made of apitch-based wax, for example) 128 is formed such that the glassprotection film 128 covers a surface of the glass layer 126 (see FIG. 2(a)). Due to the formation of the glass protection film 128, the glasslayer 126 is not brought into contact with a Ni plating solution in anelectrode forming step described later.

(f) Oxide Film Removing Step

Next, the oxide film 116 is etched using the glass protection film 128as a mask so that the oxide film 116 in an electrode forming region 130and the oxide film 124 formed on the surface of the semiconductorsubstrate on the second main surface side are removed (see FIG. 2( b)).

(g) Electrode forming step

Next, a Ni plating is applied to the semiconductor base body thusforming an anode electrode 132 in the electrode forming region 130 onthe surface of the semiconductor base body on the first main surfaceside and forming a cathode electrode 134 on the surface of thesemiconductor base body on the second main surface side (see FIG. 2(c)). The anode electrode and the cathode electrode may be formed by agas phase method such as vapor deposition or sputtering in place of Niplating.

(h) Semiconductor base body cutting step

Next, the semiconductor base body is cut by dicing or the like at acenter portion of the glass layer 126 thus dividing the semiconductorbase body into a plurality of chips whereby mesa semiconductor devices(pn diodes) 100 are manufactured (see FIG. 2( d)).

In the above-mentioned manner, it is possible to manufacture the mesasemiconductor device 100 having high reliability, an excellent switchingcharacteristic, and a low reverse leakage current IR (the semiconductordevice 100 according to the embodiment 4).

Embodiment 5

The embodiment 5 relates to a method of manufacturing a semiconductordevice.

In the same manner as the method of manufacturing a semiconductor deviceaccording to the embodiment 4, the method of manufacturing asemiconductor device according to the embodiment 5 includes, in thefollowing order: a first step of preparing a semiconductor element whichincludes a pn junction exposure portion where a pn junction is exposed;and a second step of forming a glass layer such that the glass layercovers the pn junction exposure portion. In the second step, differentfrom the method of manufacturing a semiconductor device according to theembodiment 4, the glass layer is formed such that the glass layer coversthe pn junction exposure portion with an insulation layer interposedtherebetween.

FIG. 3( a) to FIG. 3( d) and FIG. 4( a) to FIG. 4( d) are views forexplaining the method of manufacturing a semiconductor device accordingto the embodiment 5. FIG. 3( a) to FIG. 3( d) and FIG. 4( a) to FIG. 4(d) are views showing respective steps.

The method of manufacturing a semiconductor device according to theembodiment 5 includes, as shown in FIG. 3( a) to FIG. 3( d) and FIG. 4(a) to FIG. 4( d), “semiconductor base body forming step”, “trenchforming step”, “insulation layer forming step”, “heavy metal diffusionstep”, “glass layer forming step”, “glass protection film forming step”,“oxide film removing step”, “electrode forming step”, and “semiconductorbase body cutting step” in this order. Hereinafter, the method ofmanufacturing a semiconductor device according to the embodiment 5 isexplained in the order of these steps.

(a) Semiconductor base body forming step

Firstly, an n⁺ type semiconductor layer 114 is formed by diffusion of ann type impurity from a surface of an n⁻ type semiconductor layer (n⁻type silicon substrate) 110 on a second main surface side, and a p⁺ typesemiconductor layer 112 is formed by diffusion of a p type impurity froma surface of the n⁻ type semiconductor layer 110 on a first main surfaceside thus forming a semiconductor base body in which a pn junctionarranged parallel to a main surface of the semiconductor base body isformed. It may be possible that an n⁻ type semiconductor layer (n⁻ typeepitaxial layer) is formed on an n⁺ type semiconductor layer (n⁺ typesilicon substrate) and, thereafter, a p⁺ type semiconductor layer isformed by diffusion of a p type impurity from a surface of the n⁻ typesemiconductor layer (n⁻ type epitaxial layer) thus forming asemiconductor base body in which a pn junction arranged parallel to amain surface of the semiconductor base body is formed. Thereafter, oxidefilms 116, 118 are formed by thermal oxidation on a surface of the p⁺type semiconductor layer 112 and a surface of the n⁺ type semiconductorlayer 114 respectively.

(b) Trench Forming Step

Next, predetermined opening portions are formed on the oxide film 116 atpredetermined positions by photo etching. After etching the oxide film,subsequently, the semiconductor base body is etched thus formingtrenches 120 having a depth exceeding the pn junction from the surfaceof the semiconductor base body on the first main surface side (in thiscase, the trenches 120 having a depth exceeding a boundary surfacebetween the n⁻ type semiconductor layer 110 and the n⁺ typesemiconductor layer 114) (see FIG. 3( a)). Along with such formation ofthe trenches, a pn junction exposure portion A is formed on an innersurfaces of the trench.

(c) Insulation Layer Forming Step

Next, an insulation layer 136 formed of a silicon oxide film is formedon an inner surfaces of the trench 120 by a thermal oxidation methodusing dry oxygen (DryO₂) (see FIG. 3( b)). A thickness of the insulationlayer is set to a value which falls within a range of from 5 nm to 60 nm(20 nm, for example). The insulation layer is formed such that asemiconductor substrate is introduced into a diffusion furnace and,thereafter, thermal oxidation treatment is performed at a temperature of900° C. for 10 minutes while supplying an oxygen gas into the diffusionfurnace. When the thickness of the insulation layer 136 is less than 5nm, there is a case where a reverse current reduction effect cannot beacquired. On the other hand, when the thickness of the insulation layer136 exceeds 60 nm, there may be a case where a layer made of a glasscomposition cannot be formed by an electrophoresis method in a nextglass layer forming step.

(d) Heavy metal diffusion step

Next, a layer 122 which constitutes a heavy metal diffusion source isformed on a surface of the semiconductor base body on a second mainsurface side in such a manner that the oxide film 118 is removed fromthe surface of the semiconductor base body on the second main surfaceside and, thereafter, the layer made of heavy metal (Pt, for example) isformed on the surface of the semiconductor base body on the second mainsurface side by a sputtering method or by resolving heavy metal (Pt, forexample) in solution and applying the solution to the surface of thesemiconductor base body on the second main surface side by spinning.Thereafter, heavy metal is thermally diffused at a predeterminedtemperature so that the carrier recoupling center is formed in theinside of the semiconductor base body (see FIG. 3( c)). The heavy metaldiffusion step may be performed prior to the above-mentioned insulationlayer forming step or trench forming step.

(e) Glass Layer Forming Step

Next, after removing the layer 122 which constitutes the heavy metaldiffusion source, a layer made of the glass composition for protecting asemiconductor junction is formed on an inner surfaces of the trench 120and a surface of the semiconductor base body in the vicinity of thetrench 120 by an electrophoresis method, and the layer made of the glasscomposition for protecting a semiconductor junction is baked so that aglass layer 126 for passivation is formed on a surface of the trench 120(see FIG. 3( d)). Accordingly, the pn junction exposure portion A in theinside of the trench 120 is brought into a state where the pn junctionexposure portion A is covered with the glass layer 126 with theinsulation layer 136 interposed therebetween. Here, when the layer madeof the glass composition for protecting a semiconductor junction isbaked, an oxide film 124 is formed on a second main surface side of thesemiconductor base body.

(f) Glass Protection Film Forming Step

Next, a glass protection film (a glass protection film made of apitch-based wax, for example) 128 is formed such that the glassprotection film 128 covers a surface of the glass layer 126 (see FIG. 4(a)). Due to the formation of the glass protection film 128, the glasslayer 126 is not brought into contact with a Ni plating solution in anelectrode forming step described later.

(g) Oxide Film Removing Step

Next, the oxide film 116 is etched using the glass protection film 128as a mask so that the oxide film 116 formed in an electrode formingregion 130 and the oxide film 124 formed on the surface of thesemiconductor substrate on the second main surface side are removed (seeFIG. 4( b)).

(h) Electrode Forming Step

Next, a Ni plating is applied to the semiconductor base body thusforming an anode electrode 132 in the electrode forming region 130 onthe surface of the semiconductor base body on the first main surfaceside and forming a cathode electrode 134 on the surface of thesemiconductor base body on the second main surface side (see FIG. 4(c)). The anode electrode and the cathode electrode may be formed by agas phase method such as vapor deposition or sputtering in place of Niplating.

(i) Semiconductor Base Body Cutting Step

Next, the semiconductor base body is cut by dicing or the like at acenter portion of the glass layer 126 thus dividing the semiconductorbase body into a plurality of chips whereby mesa semiconductor devices(pn diodes) 102 are manufactured (see FIG. 4( d)).

In the above-mentioned manner, it is possible to manufacture a mesasemiconductor device 102 having high reliability, an excellent switchingcharacteristic, and a low reverse leakage current IR (the semiconductordevice 102 according to the embodiment 5).

Embodiment 6

The embodiment 6 relates to a method of manufacturing a semiconductordevice.

In the same manner as the method of manufacturing a semiconductor deviceaccording to the embodiment 4, the method of manufacturing asemiconductor device according to the embodiment 6 includes, in thefollowing order: a first step of preparing a semiconductor element whichincludes a pn junction exposure portion where a pn junction is exposed;and a second step of forming a glass layer such that the glass layercovers the pn junction exposure portion. In the second step, the glasslayer is formed using the glass composition for protecting asemiconductor junction according to the embodiment 1. However, differentfrom the method of manufacturing a semiconductor device according to theembodiment 4, in the embodiment 6, the first step includes a step offorming a pn junction exposure portion on a surface of a semiconductorbase body, and the second step includes a step of forming the glasslayer such that the glass layer covers the pn junction exposure portionon the surface of the semiconductor base body.

FIG. 5( a) to FIG. 5( d) and FIG. 6( a) to FIG. 6( c) are views forexplaining the method of manufacturing a semiconductor device accordingto the embodiment 6. FIG. 5( a) to FIG. 5( d) and FIG. 6( a) to FIG. 6(c) are views showing respective steps.

In the method of manufacturing the semiconductor device according to theembodiment 6, as shown in FIG. 5( a) to FIG. 5( d) and FIG. 6( a) toFIG. 6( c), “semiconductor base body preparing step”, “p⁺ typesemiconductor layer forming step”, “n⁺ type semiconductor layer formingstep”, “heavy metal diffusion step”, “glass layer forming step”, “glasslayer etching step”, “electrode forming step” and “semiconductor basebody cutting step” are carried out in this order. Hereinafter, themethod of manufacturing a semiconductor device according to theembodiment 6 is explained in the order of these steps.

(a) Semiconductor Base Body Preparing Step

Firstly, a semiconductor base body where an n⁻ type semiconductor layer(n⁻ type epitaxial layer) 212 is laminated on an n⁺ type semiconductorlayer (n⁺ type silicon substrate) 210 is prepared (see FIG. 5( a)).

(b) p⁺ Type Semiconductor Layer Forming Step

Next, after forming a mask M1 on the n type semiconductor layer 212, a ptype impurity (boron ion, for example) is implanted into a predeterminedregion on a surface of the n⁻ type semiconductor layer 212 by an ionimplantation method using the mask M1. Then, a p⁺ type semiconductorlayer 214 is formed by thermal diffusion (see FIG. 5( b)).

(c) n⁺ Type Semiconductor Layer Forming Step

Next, the mask M1 is removed from the n⁻ type semiconductor layer 212and a mask M2 is formed on the n⁻ type semiconductor layer 212.Thereafter, an n type impurity (arsenic ion, for example) is implantedinto a predetermined region on the surface of the n⁻ type semiconductorlayer 212 by an ion implantation method using the mask M2. Then, an n⁺type semiconductor layer 216 is formed by thermal diffusion (see FIG. 5(c)).

(d) Heavy Metal Diffusion Step

Next, a layer 218 which constitutes a heavy metal diffusion source isformed on a surface of the semiconductor base body on a second mainsurface side in such a manner that the mask M2 is removed and,thereafter, the layer made of heavy metal (Pt, for example) is formed onthe surface of the semiconductor base body on the second main surfaceside by a sputtering method or by resolving heavy metal (Pt, forexample) in solution and applying the solution to the surface of thesemiconductor base body on the second main surface side by spinning.Thereafter, heavy metal is thermally diffused at a predeterminedtemperature so that the carrier recoupling center is formed in theinside of the semiconductor base body (see FIG. 5( d)).

(e) Glass Layer Forming Step

Next, after removing the layer 218 which constitutes the heavy metaldiffusion source, a layer made of the glass composition for protecting asemiconductor junction is formed on a surface of the n⁻ typesemiconductor layer 212 using a paste obtained by mixing the glasscomposition for protecting a semiconductor junction according to theembodiment 1 and an organic binder by a spin coating method. Thereafter,the layer made of the glass composition for protecting a semiconductorjunction is baked thus forming a glass layer 220 for passivation (seeFIG. 6( a)).

(f) Glass Layer Etching Step

Next, after forming a mask M3 in a predetermined region on the surfaceof the glass layer 220, the glass layer is etched (see FIG. 6( b)). Dueto such etching, the glass layer 220 is formed in the predeterminedregion on the surface of the n⁻ type semiconductor layer 212.

(g) Electrode Forming Step

Next, the mask M3 is removed from the surface of the glass layer 220and, thereafter, an anode electrode 222 is formed in a region on thesurface of the semiconductor base body surrounded by the glass layer220, and a cathode electrode 224 is formed on a back surface of thesemiconductor base body (see FIG. 6( c)).

(h) Semiconductor Base Body Cutting Step

Next, the semiconductor base body is cut by dicing or the like thusdividing the semiconductor base body into a plurality of chips wherebysemiconductor devices (planar-type pn diodes) 200 are manufactured (notshown in the drawing).

In the above-mentioned manner, it is possible to manufacture aplanar-type semiconductor device 200 having high reliability (thesemiconductor device according to the embodiment 6).

Embodiment 7

The embodiment 7 relates to a method of manufacturing a semiconductordevice.

In the same manner as the method of manufacturing a semiconductor deviceaccording to the embodiment 6, the method of manufacturing asemiconductor device according to the embodiment 7 includes, in thefollowing order: a first step of preparing a semiconductor element whichincludes a pn junction exposure portion where a pn junction is exposed;and a second step of forming a glass layer such that the glass layercovers the pn junction exposure portion. In the second step, the glasslayer is formed using the glass composition for protecting asemiconductor junction according to the embodiment 1. However, differentfrom the method of manufacturing a semiconductor device according to theembodiment 6, in the embodiment 7, a semiconductor base body made of SiCis used in place of a semiconductor base body made of Si as thesemiconductor base body.

FIG. 7( a) to FIG. 10 (c) are views for explaining the method ofmanufacturing a semiconductor device according to the embodiment 7. FIG.7( a) to FIG. 7( c), FIG. 8 (a) to FIG. 8( c), FIG. 9( a) to FIG. 9( c)and FIG. 10( a) to FIG. 10( c) are views showing respective steps.

In the method of manufacturing the semiconductor device according to theembodiment 7, as shown in FIG. 7( a) to FIG. 10( c), “semiconductor basebody preparing step”, “guard ring layer forming step”, “impurityactivation step”, “back surface Ni ohmic layer forming step”, “glasslayer forming step”, “glass layer etching step”, “barrier metal layerand anode electrode layer forming step”, “cathode electrode layerforming step” and “semiconductor base body cutting step” are carried outin this order. Hereinafter, the method of manufacturing a semiconductordevice according to the embodiment 7 is explained in the order of thesesteps.

(a) Semiconductor Base Body Preparing Step

A semiconductor base body 310 which is constituted of: an n′ typesemiconductor layer (n′ type silicon carbide single crystal substrate)312 (thickness: 400 μm, impurity (nitrogen) concentration: 1×10¹⁹ cm⁻³);and an n⁻ type semiconductor layer (n⁻ type epitaxial layer/drift layer)314 (thickness: 5 μm, impurity (nitrogen) concentration: 5×10¹⁵ cm⁻³)made of silicon carbide and formed on an upper surface of the n⁺ typesemiconductor layer 312 is prepared (see FIG. 7( a)).

(b) Guard Ring Layer Forming Step

Next, a surface of the semiconductor base body 310 is cleaned and,thereafter, a silicon oxide mask M4 having an opening at a portioncorresponding to a guard ring layer 316 is formed on a surface of the n⁻type semiconductor layer 314. Then, aluminum ions which constitute ptype impurities are implanted into predetermined portion of the n⁻ typesemiconductor layer 314 using the silicon oxide mask M4 thus forming a ptype impurity introduced layer 315 (depth: 0.7 μm, p type impurityconcentration: 1×10¹⁷ cm⁻³) (see FIG. 7( b)). Aluminum ions areimplanted such that aluminum ions are implanted into the surface of then⁻ type semiconductor layer 314 in multiple stages with differentenergies (30 kev, 60 kev, . . . , 700 kev). In the guard ring layerforming step, aluminum ions may be implanted under a condition where athin silicon oxide film or the like is present in the opening formed inthe mask M4.

(c) Impurity Activation Annealing Step

Next, the mask M4 is removed and, thereafter, a protective resist layerM5 is formed on the surface (first main surface) and a back surface(second main surface) of the semiconductor base body 310 respectively(see FIG. 7( c)), and the semiconductor base body 310 is heated to atemperature of 1600° C. or above so as to activate p-type impurities.Then, the surface and back surface of the semiconductor base body 310which are made coarse in this step (see FIG. 8( a)) are subject tosacrificial oxidation in an oxygen atmosphere at a temperature of 1000°C. or above so that a sacrificial oxide film 318 is formed (see FIG. 8(b)).

(d) Back Surface Ni Ohmic Layer Forming Step

Next, the sacrificial oxide film 318 on the back surface of thesemiconductor base body 310 is removed and, thereafter, a nickel layer(thickness: 50 nm) is formed on the back surface of the semiconductorbase body 310. Then, the semiconductor base body 310 is annealed at atemperature of 950° C. thus forming a Ni ohmic layer 320 on the backsurface of the semiconductor base body 310 (see FIG. 8( c)).

(e) Glass Layer Forming Step

Next, after removing the sacrificial oxide film 318 formed on thesurface of the semiconductor base body 310 (see FIG. 9( a)), a layermade of the glass composition for protecting a semiconductor junction isformed on a surface of the semiconductor base body 310 using a pasteobtained by mixing the glass composition for protecting a semiconductorjunction according to the embodiment 1 and an organic binder by a spincoating method. Then, the layer made of the glass composition forprotecting a semiconductor junction is baked thus forming a glass layer322 for passivation (see FIG. 9( b)).

(f) Glass Layer Etching Step

Next, after forming a mask M6 on the surface of the glass layer 322, theglass layer 322 is etched (see FIG. 9( c)). Due to such etching, theglass layer 322 is formed in a predetermined region on the surface ofthe semiconductor base body 310 (see FIG. 10( a)).

(g) Barrier Metal Layer and Anode Electrode Layer Forming Step

Then, on the surface of the semiconductor base body 310, a titaniumlayer (100 nm) which constitutes barrier metal and an aluminum layer(2000 nm) which constitutes a surface electrode are sequentially formedby vapor deposition and, thereafter, etching is performed thus forming abarrier metal layer 324 and an anode electrode layer 326 (see FIG. 10(b)).

(h) Cathode Electrode Layer Forming Step

Then, a cathode electrode layer 328 which is a lamination film formed bylaminating a titanium layer, a nickel layer and a silver layer to eachother is formed on the back surface of the semiconductor base body 310.

(i) Semiconductor Base Body Cutting Step

Then, the semiconductor base body is cut by dicing or the like thusdividing the semiconductor base body into a plurality of chips wherebysemiconductor devices (planar-type Schottky-barrier diodes) 300 aremanufactured (see FIG. 10( c)).

In the above-mentioned manner, it is possible to manufacture aplanar-type semiconductor device 300 having high reliability (thesemiconductor device according to the embodiment 7).

EXAMPLES 1. Preparation of Specimens

FIG. 11 is a table showing conditions and results of examples. Glass rawmaterials are prepared to have composition ratios indicated in examples1 to 6 and comparison examples 1 and 2 (see FIG. 11). The glass rawmaterials are sufficiently mixed by a mixer and, thereafter, the mixedglass raw material is put into a platinum crucible and is melted in anelectric furnace for two hours at a predetermined temperature (examples1 to 6: 1250° C. to 1350° C., comparison examples 1 and 2: 1500° C. to1550° C.). Then, the material in a molten state is made to flow out fromthe crucible and is fed to water-cooled rolls so that glass flakes in aflaky shape are obtained. The glass flakes are pulverized by a ball milluntil the glass flakes obtain an average particle size of 5 μm thusproducing powdery glass composition.

The glass raw materials used in the examples are ZnO, SiO₂, H₃BO₃,Al₂O₃, BaCO₃, CaCO₃, MgO, ZrO₂, NiO and PbO.

2. Evaluation

The respective glass compositions obtained by the above-mentionedmethods are evaluated by the following evaluation aspects.

(1) Evaluation Aspect 1 (Environmental Burden)

The object of the present invention lies in that a semiconductor devicehaving high reliability can be manufactured by using a glass materialwhich contains no lead in the same manner as the conventional case where“a glass material containing lead silicate as a main component” is usedand hence, the score “good” is given when the glass composition containsno lead component, and the score “bad” is given when the glasscomposition contains a lead component.

(2) Evaluation Aspect 2 (Baking Temperature)

When the baking temperature is excessively high, there is a tendencythat a reverse leakage current IR is increased along with the increaseof a reverse recovery time trr. Accordingly, the score “good” is givenwhen the baking temperature is equal to or below 760° C., the score“fair” is given when the baking temperature falls within a range of from760° C. to 1100° C., and the score “bad” is given when the bakingtemperature exceeds 1100° C.

(3) Evaluation Aspect 3 (Chemical Resistance)

The score “good” is given when the glass composition exhibitsinsolubility to both aqua regia and plating solution, the score “fair”is given when the glass composition exhibits slight solubility to atleast one of aqua regia and plating solution, and the score “bad” isgiven when the glass composition exhibits solubility to at least one ofaqua regia and plating solution.

In the cases of the glass compositions for protecting a semiconductorjunction according to the examples 1 to 6, each glass compositioncontains ZnO at high concentration so that the glass composition isslightly dissolved in Ni plating solution. Accordingly, the score “fair”is given with respect to the glass compositions for protecting asemiconductor junction according to the examples 1 to 6. However, evenin these cases, by performing the Ni plating in a state where the glassprotection film is formed so as to cover a surface of the glass layer,the glass layer is not brought into contact with the Ni plating solutionand hence, there arises no serious problem.

(4) Evaluation Aspect 4 (Presence or Non-Presence of Crystallization)

A semiconductor device (pn diode) is manufactured by a methodsubstantially equal to the method of manufacturing a semiconductordevice according to the embodiment 4. As a result of the manufacture,the score “good” is given when the vitrification is achieved withoutcausing crystallization in the step of vitrification of a layer made ofa glass composition, and the score “bad” is given when the vitrificationis not achieved due to crystallization in the step of vitrification ofthe layer made of the glass composition.

(5) Evaluation Aspect 5 (Presence or Non-Presence of Generation ofBubbles)

A semiconductor device (pn diode) is manufactured by a methodsubstantially equal to the method of manufacturing a semiconductordevice according to the embodiment 4, and the observation is madewhether or not bubbles are generated in the inside of the glass layer126 (particularly, in the vicinity of a boundary surface between theglass layer 126 and the silicon substrate) in the step of vitrification(preliminary evaluation). Further, layers made of the glass compositionsfor protecting a semiconductor junction are formed on silicon substrateseach having a size of 10 mm square respectively by applying by coatingthe glass compositions for protecting a semiconductor junction accordingto the examples 1 to 6 and the comparison examples 1 and 2, and thelayers made of the glass compositions for protecting a semiconductorjunction are baked thus forming the glass layers. Then, the observationis made whether or not bubbles are generated in the inside of the glasslayers (particularly, in the vicinity of the boundary surface betweenthe glass layer and the semiconductor base body) (subsequentevaluation).

FIG. 12( a) and FIG. 12 (b) are views for explaining bubbles b generatedin the inside of the glass layer 126 in the preliminary evaluation. FIG.12( a) is a cross-sectional view of a semiconductor device when nobubbles bare generated, while FIG. 12( b) is a cross-sectional view of asemiconductor device when the bubbles b are generated. FIG. 13( a) andFIG. 13( b) are photographs for explaining the bubbles b generated inthe inside of the glass layer 126 in the subsequent evaluation. FIG. 13(a) is a photograph showing a boundary surface between the semiconductorbase body and the glass layer when no bubbles are generated in anenlarged manner, while FIG. 13( b) is a photograph showing a boundarysurface between the semiconductor base body and the glass layer when thebubbles are generated in an enlarged manner. As a result of theexperiment, it is found that there is favorable correlation between theresult of the preliminary evaluation and the result of the evaluation ofthe present invention. In the subsequent evaluation, the score “good” isgiven when no bubble having a diameter of 50 μm or more is generated inthe inside of the glass layer, the score “fair” is given when one totwenty bubbles having a diameter of 50 mm or more are generated in theinside of the glass layer, and the score “bad” is given when twenty oneor more bubbles having a diameter of 50 μm or more are generated in theinside of the glass layer.

In the case of the glass composition for protecting a semiconductorjunction according to the example 1, the glass composition contains nonickel oxide so that a slight amount of bubbles is generated whereby thescore “fair” is given. However, even in the case where the glasscomposition contains no nickel oxide, by manufacturing a semiconductordevice by a method substantially equal to the method of manufacturing asemiconductor device according to the embodiment 5 (that is, the methodof manufacturing a semiconductor device where a glass layer is formed ona pn junction surface with an insulation layer interposed therebetween),no bubbles are generated.

(6) Evaluation Aspect 6 (Reverse Leakage Current)

A semiconductor device (pn diode) is prepared by a method substantiallyequal to the method of manufacturing a semiconductor device according tothe embodiment 4, and a reverse characteristic of the preparedsemiconductor device is measured. FIG. 14 is a graph showing a reverseleakage current in the semiconductor device which is prepared using theglass composition for protecting a semiconductor junction according tothe example 3. As the result of the measurement, the score “good” isgiven in the case where a reverse leakage current is 1 μA or less when areverse voltage VR of 200V is applied, while the score “bad” is given inthe case where the reverse leakage current exceeds 1 μA when the reversevoltage VR of 200V is applied.

(7) Evaluation Aspect 7 (Reverse Recovery Time TRR)

Semiconductor devices (pn diodes) are prepared by a method substantiallyequal to the method of manufacturing a semiconductor device according tothe embodiment 4 using the glass composition for protecting asemiconductor junction of the example 4 and the glass composition forprotecting a semiconductor junction of the comparison example 1, and areverse recovery time trr are measured. The baking condition of theglass layer is set such that the glass layer is baked at a temperatureof 720° C. for 15 minutes when the glass composition for protecting asemiconductor junction according to the example 4 is used, and the glasslayer is baked at a temperature of 870° C. for 15 minutes when the glasscomposition for protecting a semiconductor junction according to thecomparison example 1 is used.

FIG. 15 is a graph for explaining a method of measuring a reverserecovery time trr. The measurement of the reverse recovery time isperformed such that, as shown in FIG. 15, a drive voltage is applied toa semiconductor device under a condition that a reverse current of 100mA flows at maximum when the semiconductor device is turned off (reversevoltage VR=50V) from an ON state where a forward current of 100 mA issupplied to the semiconductor device. That is, as shown in FIG. 15, thereverse recovery time trr is measured as a time from a point of timethat the forward current IF is dropped to 0 mA after the semiconductordevice is turned off to a point of time that a reverse current IR isattenuated to a value which is 10% of a maximum value (90% recoverytime).

As a result of the measurement, it is found that while the reverserecovery time trr is 43.6 ns when the glass composition for protecting asemiconductor junction according to the comparison example 1 is used,the reverse recovery time trr is 39.6 ns when the glass composition forprotecting a semiconductor junction according to the example 4 is used.That is, it is found that the reverse recovery time trr when the glasscomposition for protecting a semiconductor junction according to theexample 4 is used is shorter than the reverse recovery time trr when theglass composition for protecting a semiconductor junction according tothe comparison example 1 is used by approximately 10%. Based on thisresult, the score “good” is given to the glass composition forprotecting a semiconductor junction according to the example 4, and thescore “fair” is given to the glass composition for protecting asemiconductor junction according to the comparison example 1. Thisresult implies that with the use of the glass composition for protectinga semiconductor junction according to the example 4, a bakingtemperature can be lowered and hence, the carrier recoupling center ishardly decreased by annealing in baking a layer made of the glasscomposition for protecting a semiconductor junction.

(8) Comprehensive Evaluation

(8-1) Comprehensive Evaluation 1

The score “good” is given when the score “good” is given with respect toall of the above-mentioned evaluation aspects 1 to 7. The score “fair”is given when the score “fair” is given with respect to at least one ofthe above-mentioned evaluation aspects 1 to 7. The score “bad” is givenwhen the score “bad” is given with respect to at least one of theabove-mentioned evaluation aspects 1 to 7.

(8-2) Comprehensive Evaluation 2

With respect to the evaluation aspect 3 (chemical resistance), when theNi plating is performed in a state where the glass protection film isformed so as to cover the surface of the glass layer, the glass layer isnot brought into contact with the Ni plating solution and hence, noserious problem arises. Accordingly, by taking into account this fact,the glass compositions for protecting a semiconductor junction accordingto the examples 2 to 6 have no problem with respect to all evaluationaspects and hence, the score “good” is given with respect to the glasscompositions for protecting a semiconductor junction according to theexamples 2 to 6.

(8-3) Comprehensive Evaluation 3

In the same manner as the above-mentioned comprehensive evaluation 2,with respect to the evaluation aspect 3 (chemical resistance), when theNi plating is performed in a state where the glass protection film isformed so as to cover the surface of the glass layer, the glass layer isnot brought into contact with the Ni plating solution and hence, noserious problem arises. Also with respect to the evaluation aspect 6(generation of bubbles), when a semiconductor device is manufactured bya method substantially equal to the method of manufacturing asemiconductor device according to the embodiment 5, no bubbles aregenerated. Accordingly, by taking into account this fact, the glasscompositions for protecting a semiconductor junction according to theexamples 1 to 6 have no problem with respect to all evaluation aspectsand hence, the score “good” is given with respect to the glasscompositions for protecting a semiconductor junction according to theexamples 1 to 6.

3. Evaluation Result

As can be understood also from FIG. 11, with respect to the glasscomposition according to the comparison example 1, the score “fair” isgiven with respect to the evaluation aspects 2 and 7 and the score“fair” is given with respect to all comprehensive evaluations 1 to 3.With respect to the glass composition according to the comparisonexample 2, the score “bad” is given with respect to the evaluationaspect 1 and the score “fair” is given with respect to the evaluationaspect 2 so that the score “bad” is given with respect to thecomprehensive evaluation.

To the contrary, with respect to the glass compositions for protecting asemiconductor junction according to the examples 2 to 6, although thescore “fair” is given with respect to the evaluation aspect 3(accordingly, the score “fair” is given with respect to thecomprehensive evaluation 1), the score “good” is given with respect tothe evaluation aspects other than the evaluation aspect 3. In view ofthe above, it is found that, with respect to the glass composition forprotecting a semiconductor junction according to the examples 2 to 6,provided that a semiconductor device is manufactured under a conditionthat a glass protection film is used in etching the oxide film, thesemiconductor device can be manufactured with no problem (accordingly,the score “good” is given with respect to the comprehensive evaluation2).

Further, with respect to the glass composition for protecting asemiconductor junction according to the example 1, although the score“fair” is given with respect to the evaluation aspects 3 and 5(accordingly, the score “fair” is given with respect to thecomprehensive evaluation 1), the score “good” is given with respect tothe evaluation aspects other than the evaluation aspects 3 and 5. Inview of the above, it is found that, with respect to the glasscomposition for protecting a semiconductor junction according to theexample 1, provided that a semiconductor device is manufactured underconditions that a glass protection film is used in etching the oxidefilm and a glass layer is formed on a pn junction surface with aninsulation layer interposed therebetween, the semiconductor device canbe manufactured with no problem (accordingly, the score “good” is givenwith respect to the comprehensive evaluation 3).

Although the glass composition for protecting a semiconductor junction,the method of manufacturing a semiconductor device and such asemiconductor device according to the present invention have beenexplained heretofore in conjunction with the above-mentionedembodiments, the present invention is not limited to the above-mentionedembodiments, and can be carried out without departing from the gist ofthe present invention. For example, the following modifications areconceivable.

(1) In the above-mentioned embodiments 4 to 6, examples where thepresent invention is applied to the method of manufacturing asemiconductor device which uses a semiconductor base body made of Si areexplained and, in the embodiment 7, an example where the presentinvention is applied to the method of manufacturing a semiconductordevice which uses a semiconductor base body made of SiC is explained.However, the present invention is not limited to such examples. Thepresent invention is also applicable to a method of manufacturing asemiconductor device which uses a semiconductor base body made of GaN.

(2) In the above-mentioned embodiments 1 and 3, although nickel oxide isused as a defoaming agent, the present invention is not limited tonickel oxide. In place of nickel oxide, copper oxide, manganese oxide orzirconium oxide may be used, for example.

(3) Although the present invention relates to “the glass composition forprotecting a semiconductor junction which substantially contains none ofPb, As, Sb, Li, Na and K”, the present invention also includes “a glasscomposition for protecting a semiconductor junction which substantiallycontains none of Pb, P, As, Sb, Li, Na and K”.

(4) In the above-mentioned embodiments 4 and 5, although the layer madeof the glass composition for protecting a semiconductor junction isformed by the electrophoresis method in the glass layer forming step,the present invention is not limited to such a method. The layer made ofthe glass composition for protecting a semiconductor junction may beformed by a spin coating method, a screen printing method or a doctorblade method. In this case, the layer made of the glass composition forprotecting a semiconductor junction is formed using a paste obtained bymixing the glass composition for protecting a semiconductor junctionaccording to the embodiment 1 and an organic binder as the glasscomposition for protecting a semiconductor junction.

(5) In the above-mentioned embodiments 6 and 7, although the layer madeof the glass composition for protecting a semiconductor junction isformed by the spin coating method in the glass layer forming step, thepresent invention is not limited to such a method. The layer made of theglass composition for protecting a semiconductor junction may be formedby a screen printing method or a doctor blade method. Further, the layermade of the glass composition for protecting a semiconductor junctionmay be formed by the electrophoresis method. In the latter case, thelayer made of the glass composition for protecting a semiconductorjunction is formed using the glass composition for protecting asemiconductor junction according to the embodiment 1 as the glasscomposition for protecting a semiconductor junction without mixing theglass composition for protecting a semiconductor junction according tothe embodiment 1 with the organic binder.

(6) In the above-mentioned respective embodiments, the present inventionhas been explained by taking the diode (the mesa-type pn diode, theplanar-type pn diode or the planar-type Schottky-barrier diode) as anexample. However, the present invention is not limited to such examples.The present invention is also applicable to any kinds of semiconductordevices where a pn junction is exposed (thyristors, power MOSFETs, IGBTsand the like, for example).

EXPLANATION OF SYMBOLS

-   100, 102, 200, 300, 900: semiconductor device, 110,910: n⁻ type    semiconductor layer, 112, 912: p type semiconductor layer, 114, 914:    n⁺ type semiconductor layer, 116, 118, 124, 916, 918, 924: oxide    film, 120, 920: trench, 122, 922: film constituting heavy metal    diffusion source, 126, 926: glass layer, 128, 928: glass protection    film, 130, 930: electrode forming region, 132, 932: anode electrode,    134, 934: cathode electrode, 136: insulation layer, 210: n⁺ type    semiconductor layer, 212: n⁻ type semiconductor layer, 214: p⁺ type    semiconductor layer, 216: n⁺ type semiconductor region, 218: film    constituting heavy metal diffusion source, 220: glass layer, 222:    anode electrode layer, 224: cathode electrode layer, 310:    semiconductor base body, 312: n⁺ type semiconductor layer, 314: n⁻    type semiconductor layer, 316: guard ring layer, 318: sacrificial    oxide film, 320: Ni ohmic layer, 322: glass layer, 324: barrier    metal layer, 326: anode electrode layer, 328: cathode electrode    layer, M1,M2,M3,M4,M6: mask, M5: protective resist

The invention claimed is:
 1. A method of manufacturing a semiconductordevice comprising, in the following order: a first step of preparing asemiconductor element having a pn junction exposure portion where a pnjunction is exposed; and a second step of forming a glass layer suchthat the glass layer covers the pn junction exposure portion, wherein inthe second step, the glass layer is formed using a glass composition forprotecting a semiconductor junction made of fine glass particlesprepared from a material in a molten state obtained by melting a glassraw material which contains at least ZnO, SiO₂, B₂O₃, Al₂O₃ and at leasttwo oxides of alkaline earth metals selected from a group consisting ofBaO, CaO and MgO with the following contents and substantially containsnone of Pb, As, Sb, Li, Na and K, the glass composition for protecting asemiconductor junction containing no filler. ZnO: 30 mol % to 60 mol %SiO₂: 5 mol % to 45 mol % B₂O₃: 5 mol % to 30 mol % Al₂O₃: 5 mol % to 13mol % oxide of alkaline earth metal: 1 mol % to 10 mol %.
 2. The methodof manufacturing a semiconductor device according to claim 1, whereinthe second step comprises a step of forming an insulation film on the pnjunction exposure portion, and a step of forming the glass layer suchthat the glass layer covers the pn junction exposure portion with theinsulation film interposed therebetween.
 3. A semiconductor devicecomprising: a semiconductor element having a pn junction exposureportion where a pn junction is exposed; and a glass layer which isformed such that the glass layer covers the pn junction exposureportion, wherein the glass layer is formed using a glass composition forprotecting a semiconductor junction made of fine glass particlesprepared from a material in a molten state obtained by melting a glassraw material which contains at least ZnO, SiO₂, B₂O₃, Al₂O₃ and at leasttwo oxides of alkaline earth metals selected from a group consisting ofBaO, CaO and MgO with the following contents and substantially containsnone of Pb, As, Sb, Li, Na and K, the glass composition for protecting asemiconductor junction containing no filler. ZnO: 30 mol % to 60 mol %SiO₂: 5 mol % to 45 mol % B₂O₃: 5 mol % to 30 mol % Al₂O₃: 5 mol % to 13mol % oxide of alkaline earth metal: 1 mol % to 10 mol %.
 4. Thesemiconductor device according to claim 3, wherein the glass layer isformed such that the glass layer covers the pn junction exposure portionwith an insulation layer interposed therebetween.
 5. A glass compositionfor protecting a semiconductor junction used in forming a glass layerwhich protects a pn junction in a semiconductor element having a pnjunction exposure portion where the pn junction is exposed, wherein theglass composition for protecting a semiconductor junction is made offine glass particles prepared from a material in a molten state obtainedby melting a glass raw material which contains at least ZnO, SiO₂, B₂O₃,Al₂O₃ and at least two oxides of alkaline earth metals selected from agroup consisting of BaO, CaO and MgO with the following contents andsubstantially contains none of Pb, As, Sb, Li, Na and K, the glasscomposition for protecting a semiconductor junction containing nofiller. ZnO: 30 mol % to 60 mol % SiO₂: 5 mol % to 45 mol % B₂O₃: 5 mol% to 30 mol % Al₂O₃: 5 mol % to 13 mol % oxide of alkaline earth metal:1 mol % to 10 mol %.
 6. The glass composition for protecting asemiconductor junction according to claim 5, wherein the glass rawmaterial further contains nickel oxide.
 7. The glass composition forprotecting a semiconductor junction according to claim 5, wherein theglass raw material further contains ZrO₂.
 8. The glass composition forprotecting a semiconductor junction according to claim 5, wherein aglass transition temperature Tg falls within a range of from 540° C. to680° C.
 9. The glass composition for protecting a semiconductor junctionaccording to claim 5, wherein the content of ZnO falls within a range offrom 40 mol % to 56 mol %, the content of SiO₂ falls within a range offrom 8 mol % to 20 mol %, the content of B₂O₃ falls within a range offrom 20 mol % to 30 mol %, the content of Al₂O₃ falls within a range offrom 6 mol % to 10 mol %, and the content of the oxide of an alkalineearth metal falls within a range of from 2 mol % to 5 mol %.
 10. Theglass composition for protecting a semiconductor junction according toclaim 5, wherein the semiconductor element is a semiconductor elementmade of SiC.
 11. The glass composition for protecting a semiconductorjunction according to claim 1, wherein the semiconductor element is asemiconductor element made of GaN.
 12. The glass composition forprotecting a semiconductor junction according to claim 5, wherein theglass raw material substantially contains no Bi.
 13. The glasscomposition for protecting a semiconductor junction according to claim12, wherein the glass raw material substantially contains no P.
 14. Theglass composition for protecting a semiconductor junction according toclaim 5, wherein the glass layer is a glass layer which is formed suchthat the glass layer covers the pn junction exposure portion with aninsulation layer interposed therebetween.
 15. The glass composition forprotecting a semiconductor junction according to claim 14, wherein anaverage linear expansion coefficient within a temperature range of from50° C. to 500° C. falls within a range of from 4.5×10⁻⁶ to 5.8×10⁻⁶. 16.The glass composition for protecting a semiconductor junction accordingto claim 1, wherein the semiconductor element is a semiconductor elementmade of Si.
 17. The glass composition for protecting a semiconductorjunction according to claim 16, wherein the semiconductor element is afast recovery diode.